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Growing watermelons in the home garden makes for visual delight and a juicy, refreshing harvest. Although these warm-season crops appear quite sturdy, they are susceptible to a wide variety of pest problems. Protect your garden from cosmetic damage and crop loss by monitoring plants regularly for pests or symptoms of infestations. Put a control program in place immediately if pests make an appearance on your watermelons.

Preventive Care

Healthy watermelons are typically better prepared than neglected melons to fight off and overcome problems with pests. Watermelons thrive in areas of the garden that offer full sunlight. These fruiting plants need moist, well-drained, sandy loam or silt loam soil. Drip irrigation will provide the regular watering watermelons need without either creating wet conditions or allowing drought to occur. Gardeners should irrigate to a depth of 6 inches.

Cutworms

Cutworms are 1 1/2-inch-long moth larvae (caterpillars) that typically destroy seedlings by cutting them off at the soil line. To control these pests, which generally already are present in the soil when watermelons are planted, check plants daily for their presence. Keep your garden free of weeds and debris that provide hiding places for cutworms. For an extremely mild problem, gardeners can effectively pluck worms off plants by hand and destroy them. For widespread problems, applications of an insecticide with an active ingredient such as carbaryl offers effective control.

Sucking Pests

Sucking pests feed on watermelon plant sap that they remove from the plant's tender tissue. Most of these pests secrete a sticky-sweet liquid called honeydew. When honeydew lands on plant parts, it encourages the growth of a black fungus called sooty mold. Though sooty mold does not infect plants, it blocks out essential sunlight. Melon aphids are sucking pests of watermelons that display soft, pear-shaped, wingless bodies. They are most active during warm weather. Their feeding may distort and curl the plant's leaves and introduce viruses. Whiteflies have tiny bodies with white wings. They are difficult to see without magnification. Gardeners may tap on a leaf to watch for the tiny cloud of white pests that will hover over disturbed foliage. Whitefly feeding may lead to rotting of internal watermelon flesh and death just before harvest as a result of virus transmission. Spider mites are sucking pests that are so small that they look like specks. The webs they spin, much like spiders, are the tell-tale sign of their presence. Foliage often takes on tiny, discolored dots, then turns bronze. Fruit usually remains healthy, though it is often covered with webbing.

Sucking Pest Control

Gardeners should first release natural enemies onto watermelon plants to control pest populations. Lacewings and parasitic wasps attack aphids and whiteflies, while lacewing larvae and western predatory mites attack spider mites. For further control, gardeners may saturate plants with low-toxicity insecticidal soap or oils to kill pests on contact. For more aggressive treatment, applications of a higher-toxicity insecticide with an active ingredient such as azadirachtin will control these sucking bugs.

Rindworms

Rindworms are caterpillars that feed on melon rinds. Common infestations on watermelons include cabbage loopers and beet armyworms. These pests may also eat foliage. Cabbage loopers hump their backs as they scoot their back segment forward during movement, giving them their characteristic "loop" appearance. When mature, larvae measure 1 1/4 inches long. Beet armyworms display "dull green" bodies with "wavy, light-colored stripes lengthwise down the back and broader stripes on each side," according to the University of Florida Institute of Food and Agricultural Sciences Extension. Damage includes discolored spots on rinds. To control rindworms, gardeners should release natural enemies, such as parasitic wasps and green lacewings. For further control, applications of the microbial insecticide B.t. (Bacillus thuringiensis) or chemical-based insecticides with the active ingredient methoxyfenozide offer control.

Tunneling Insects

Liromyzid leafminers of the Liriomyza species attack watermelon plants by tunneling into melon leaf surfaces, creating visible channels. The yellow larvae are extremely tiny and difficult to see with the naked eye. However, their damage is visible, including white, haphazard tunnels on upper and lower leaf surfaces and occasionally dried leaves that drop from the plant, sun-scalded fruit and plant death. To control these pests, gardeners may release parasitic eulophid wasps, which offer effective management of the pest population.

Boring Bugs

Darkling beetles pose a significant problem on watermelons. Measuring up to 1/4 inch in length, adult beetles display dark brown, blue or black bodies. The larvae, often called false wireworms, are yellow to brown with tiny, thin bodies. Pests tunnel into watermelon fruit or feed on foliage, potentially leading to major crop loss. To control these pests, gardeners should pull weeds from the area surrounding the melons and may apply a pesticide with an active ingredient such as malathion.

About the Author

Tarah Damask's writing career began in 2003 and includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum and articles for various websites. Damask holds a Master of Arts in English and creative writing from the University of North Texas.